Biomass conversion systems providing integrated stabilization of a hydrolysate using a slurry catalyst following biomass pretreatment and methods for use thereof

Abstract

Digestion of cellulosic biomass solids to form a hydrolysate may be conducted with integrated catalytic reduction during digestion to transform soluble carbohydrates in the hydrolysate into a more stable reaction product. Such integrated catalytic reduction may be conducted using a slurry catalyst. Biomass conversion systems for performing integrated catalytic reduction can comprise: a hydrothermal digestion unit that contains a slurry catalyst capable of activating molecular hydrogen; an optional hydrogen feed line that is operatively connected to the hydrothermal digestion unit; a fluid circulation loop comprising the hydrothermal digestion unit and a catalytic reduction reactor unit, the catalytic reduction reactor unit also containing the slurry catalyst; a pretreatment digestion unit that is not part of the fluid circulation loop and does not contain the slurry catalyst; and a solids transport mechanism operatively connecting the pretreatment digestion unit to the hydrothermal digestion unit.

I claim: 
     
         1 . A method comprising:
 providing cellulosic biomass solids in a pretreatment digestion unit;   heating the cellulosic biomass solids in the pretreatment digestion unit at a first temperature in a range of 100° C. and 160° C. for a first time period of 4 hours or less, the first temperature and the first time period being sufficient to remove at least a portion of the hemicellulose and lignins from the cellulosic biomass solids, thereby producing a biomass pulp;   transferring at least a portion of the biomass pulp to a hydrothermal digestion unit that contains a slurry catalyst capable of activating molecular hydrogen;   heating the biomass pulp in the hydrothermal digestion unit at a second temperature in a range of 160° C. and 260° C. for a second time period of 1 hour or more in the presence of molecular hydrogen while circulating the slurry catalyst therethrough, the second temperature and the second time period being sufficient to digest at least a portion of the cellulose, thereby forming a hydrolysate comprising soluble carbohydrates within a liquor phase and   wherein the first time period is shorter than the second time period;   at least partially transforming the soluble carbohydrates into a reaction product via a catalytic reduction reaction while the soluble carbohydrates are within the hydrothermal digestion unit; and   transferring at least a portion of the liquor phase to a catalytic reduction reactor unit that also contains a slurry catalyst capable of activating molecular hydrogen; wherein the slurry catalyst in the hydrothermal digestion unit and the catalytic reduction reactor unit comprises a particulate size of about 250 microns or less.   
     
     
         2 . The method of  claim 1 , further comprising:
 recirculating at least a portion of the liquor phase from the catalytic reduction reactor unit to the hydrothermal digestion unit.   
     
     
         3 . The method of  claim 2 , wherein the liquor phase is recirculated to the hydrothermal digestion unit at a recycle ratio in a range of 0.2 and 10. 
     
     
         4 . The method of  claim 2 , wherein the liquor phase is recirculated to the hydrothermal digestion unit at a recycle ratio of 2 or less. 
     
     
         5 . The method of  claim 3 , wherein the liquor phase is recirculated to the hydrothermal digestion unit such upward fluid flow is established therein. 
     
     
         6 . The method of  claim 1 , wherein, after heating to the second temperature and for the second time period, less than 10% of the cellulosic biomass solids, on a dry basis, remains undigested. 
     
     
         7 . The method of  claim 1 , wherein the liquor phase is transferred from the hydrothermal digestion unit to the catalytic reduction reactor unit such that the liquor phase flows upwardly in the catalytic reduction reactor unit. 
     
     
         8 . The method of  claim 1 , further comprising:
 removing the hemicellulose and lignins from the pretreatment digestion unit before transferring the biomass pulp to the hydrothermal digestion unit.   
     
     
         9 . The method of  claim 1 , further comprising:
 after further transforming the soluble carbohydrates into the reaction product, withdrawing a portion of the reaction product from the catalytic reduction reactor unit, wherein the withdrawing is achieved at least via a reaction product takeoff line in fluid communication with the fluid circulation loop, the reaction product takeoff line being located between the hydrothermal digestion unit and an outlet of the catalytic reduction reactor unit; and   converting the reaction product into a biofuel.   
     
     
         10 . The method of  claim 9 , further comprising:
 separating solids from the reaction product after withdrawing, wherein said separating is achieved with a solids separation mechanism that is operatively connected to the reaction product takeoff line.   
     
     
         11 . The method of  claim 1 , wherein the slurry catalyst comprises a poison-tolerant catalyst. 
     
     
         12 . The method of  claim 1 , wherein the slurry catalyst is operable to generate molecular hydrogen. 
     
     
         13 . The method of  claim 1  wherein the slurry catalyst is regenerable through exposure to water having a temperature of at least about 200 degrees C. 
     
     
         14 . The method of  claim 1  wherein the providing cellulosic biomass solids to the hydrothermal digestion unit comprises using a solids introduction mechanism that is operatively connected to the hydrothermal digestion unit, the solids introduction mechanism comprising an atmospheric pressure zone and a pressure transition zone that cycles between atmospheric pressure and a higher pressure state.